Question

$\text{The oxidation number of iron in the compound formed during brown ring test for NO}_3^-\text{ ion is \_\_\_\_\_\_.}$

Answer 1

Correct Answer: 1

The oxidation number of iron in the compound formed during the brown ring test for nitrate ion (NO₃^-) requires understanding the chemical reaction. The brown ring test reacts nitrates with ferrous sulfate (FeSO₄) and concentrated sulfuric acid, forming a brown ring complex. In this complex, the nitrate ion is reduced, and iron is integral to its formation.
The chemical equation for the brown ring complex is:
\[ [Fe(H_2O)_5NO]^{2+} \] 
Iron is in a low oxidation state within this complex. Its oxidation state is determined as follows:

1. The complex ion is [Fe(H₂O)₅NO]²⁺.
2. Let x represent the oxidation number of Fe.
3. The nitrosyl (NO) group is a neutral ligand with a charge of 0.
4. Each water molecule is neutral, contributing 0.
5. The overall charge of the complex is +2. The equation is formulated as: \( x + 0 \times 5 + 0 = +2 \).
6. Solving yields \( x = +1 \).

Therefore, the oxidation number of iron in the brown ring compound is +1. 
The range check (1,1) confirms +1 as the correct and sole possible value.